Constant velocity joints are common components in automotive vehicles. Typically, constant velocity joints are employed where transmission of a constant velocity rotary motion is desired or required. Common types of constant velocity joints include end motion or plunging and fixed motion designs. Of particular interest is the end motion or plunging type constant velocity joints, which include a tripod joint, a double offset joint, a cross groove joint, and a cross groove hybrid. Of these plunging type joints, the tripod type constant velocity joint uses rollers as torque transmitting members, and the others use balls as torque transmitting members. Typically, these types of joints are used on the inboard (toward the center of the vehicle) on front sideshafts and on the inboard or outboard side for sideshafts on the rear of the vehicle and on the propeller shafts found in rear wheel drive, all wheel drive, and four-wheel drive vehicles.
Propeller shafts are commonly used in motor vehicles to transfer torque and rotational movement from the front of the vehicle to a rear axle differential such as in a rear wheel and all wheel drive vehicles. Propeller shafts are also used to transfer torque and rotational movement to the front axle differential in four-wheel drive vehicles. In particular, two-piece propeller shafts are commonly used when larger distances exist between the front drive unit and the rear axle of the vehicle. Similarly, sideshafts are commonly used in motor vehicles to transfer torque from a differential to the wheels. The propeller shaft and sideshafts are connected to their respective driving input and output components by a joint or series of joints. Joint types used to connect the propeller shaft and sideshaft interconnecting shafts include Cardan, Rzeppa, tripod and various ball type joints.
In addition to transferring torque and rotary motion, in many automotive vehicles the propeller shaft and axle drives allow for axial motion. Specifically, axial motion is designed into two-piece propeller shafts by using an end motion or plunging type constant velocity joint.
Besides transferring mechanical energy and accommodating axial movement, it is desirable for plunging constant velocity joints to have adequate crash-worthiness. In particular, it is desirable for the constant velocity joint to be shortened axially preventing the propeller shaft from buckling, penetrating the passenger compartment, or damaging other vehicle components in close proximity of the propeller shaft or drive axle. In many crash situations, the vehicle body shortens and deforms by absorbing energy that reduces the vehicle acceleration; further protecting the occupants and the vehicle. As a result, it is desirable for the propeller shaft be able to reduce in length during the crash, allowing the constant velocity joint to travel beyond its operation length. It is also desirable for the constant velocity joint within the propeller shaft to absorb a considerable amount of the deformation energy during the crash. Propeller shaft length reduction during a crash situation is often achieved by having the propeller shaft telescopically collapse and energy absorb thereafter.
In telescopic propeller shaft assemblies, the joint must translate beyond the constant velocity joint limitation before the telescopic nature of the propeller shaft is effectuated. In some designs, the propeller shaft must translate the torque as well as maintain the ability to telescope. In other designs, the telescopic nature of the joint only occurs after destruction of the joint, joint cage or some type of joint retaining ring. Still in other designs, the joint must first translate the balls off the race area before the telescopic attribute can be used for axial joint displacement. The limitation of the telescopic ability is that the constant velocity joint must be compromised before axial displacement can occur in a crash situation. Therefore, there is a desire to have a constant velocity joint that can accommodate the axial displacement during a crash.
Furthermore, the energy absorption only occurs after the functional limit or end of the constant velocity joint has been surpassed. This causes a time delay in the energy absorption of the propeller shaft. Then and only then, the energy absorption is accomplished and typically has a force step or impulse energy absorption pattern. After the initial energy absorption, typically, there is no further energy absorption in the propeller shaft. In another situation there is further energy absorption, but only after the joint balls successfully translate off the joint race and onto the propeller shaft. Therefore, there is a desire to have a constant velocity joint that has a controlled or tuned force energy absorption profile over a range of the joint's axial travel distance, especially when the normal operational range of the joint has been surpassed.
It would be advantageous to have the above mentioned features in the double offset joint. The double offset constant velocity joint is commonly known by automotive manufactures and suppliers as a DO type joint and the invention, here below, relates to this type of joint. Double offset joints are used for accommodating angular and axial displacements in a propeller shaft. Propeller shafts, in turn, are used to connect a drive unit, i.e. transmission, to a rear differential. The differential has an outer joint part in which a plurality of linear ball tracks are axially formed on an inner cylindrical surface thereof. This outer joint part contains an inner joint part in which a plurality of linear ball tracks are axially formed on an outer spherical surface thereof and an equal number of torque transmitting balls retained by cage windows in a ball cage and located in a pair of outer and inner ball tracks. Since the spherical center of the outer spherical face of the cage and the spherical center of the inner concave face thereof are offset to the opposite side in the axial direction from the center of the cage windows, they are called “double offset type”. When this kind of joint transmits a torque while taking an operating angle, the cage rotates to the position of the torque transmitting balls moving in the ball tracks in response to the inclination of the inner joint part to retain the torque transmitting balls on the constant velocity plane bisecting the operating angle. Furthermore, as the outer joint part and the inner joint part relatively displace in the axial direction, a slipping occurs between the outer spherical face of the cage and the inner cylindrical surface of the outer joint part to ensure a smooth axial displacement (plunging).